Blanching Flashcards
Define blanching
The scalding of vegetables in boiling water or steam for a short time, followed by a quick cooling in ice water
Examples of blanched products
Potato chips, tomato sauce, frozen broccoli
What is the purpose of blanching?
1 - inactivate enzymes that break down/change the food during storage
2 - pretreatment after prep of raw material before dehydration/freezing/heat sterilization
3 - peeling (corn husking / wilt blanching)
4 - reduced microbial load
How does blanching deactivate enzymes?
Denature the proteins (change the structure)
What happens to enzymes under refrigeration
enzymes still active, but slower ( still stable but become dormant)
What happens when you thaw refrigerated blanched produce?
enzymes and substrates come in contact and can denature
Describe applications of blanching, with regards to enzyme deactivation
1 - Dehydrated foods - stable but slow enzymes (low moisture and dehydration temp cannot guarantee enzyme deactivation)
2 - Canned foods - enzymes active before blanching/ high thermal process
List the type of enzymes:
1 - Polyphenol oxidase (PPO, phenolase)
2- Catalase
3 - Pectic enzymes
4- Lipase
5 - Lipoxygenase
6- Ascorbic acid oxidase
7-peroxidase
Can blanching activate enzymes? Can it be beneficial?
Yes, it can stabilize veg structure before canning
How do you inactivate Polyphenol oxidase?
- Rapid inactivation -> higher than 80C (90C / 8s)
- lower pH
- sulfite treatment
-presoak in salt solution (0.1% NaCl)
How do you inactivate pectin methylesterase (PME) and polygalacturonase (PG)
PME = 170F / 1min
PG = 195F / 1min
What is the role of lipase?
Breakdown of lipids (ie. fish, milk)
(triglyceride -> glycerol -> free fatty acid)
What is the role of Lipoxygenase?
Oxygenation of unsaturated fatty acids (off-flavour)
Chlorophylls = bleaching effect
How do you denature Lipoxygenase?
1 - 180F / 3 min
2 - pH 2 (irreversible)
What is the role of ascorbic acid oxidase?
Destroy ascorbic acid (lessen vit C activity)
How do you inactivate Ascorbic acid oxidase?
- low temps
- heat
- de-aeration
How do you determine how long to blanch to deactivate Peroxidase?
- ## Check peroxidase activity
What is the role of peroxidase?
1 - vitamin C oxidation
2 - carotenoids bleaching
3 - anthocyanin decoloring
4 - FFA oxidation
FFA oxidation creates off-flavour
What is significant about monitoring peroxidase?
Indicates blanching efficiency
How do you inactivate Peroxidase?
180 - 190 F / 3 min
Which enzymes in fruits and veg affect 1: colour, 2: flavour, 3: texture, 4: vitamin C
1 - PPO, peroxidase
2 - Catalase, lipase, lipoxigenase, peroxidase
3 - Pectic enzymes
4 - ascorbic acid oxidase, peroxidase
What factors affect blanching?
additional description included
- Type of product (kinetics of the enzyme)
- size of product pieces
- thermal conductivity of product
- temp
- time
What are the consoquences of incomplete blanching?
- high microbial load
- active enzymes left
- insufficient textural change
What are the conciquences of over-blanching?
1 - Texture change
2 - Degradation of bioactive compounds (vit C deactivated)
3 - Too much moisture (vit C leeches out)
Should blanch <2 min
Describe a steam blancher
Chamber box or tunnel where the food is exposed to steam
Usually food is on a screen or mesh conveyor
Steam blancher
What does the length of the tunnel depend on?
- Conveyor speed
- Blanch time required
Steam blancher
What does the product depth bed affect? Why is it important?s
Important to heat transfer
Steam Blancher
What is the function of the rotary locks?
- Retain steam
- Hold temp
Steam blancher
How can you improve uniformity?
Use fans to push the steam through the food
Steam blancher
Describe the advantages and disadvantages:
**Advantages **= easy to clean + sterilize
Disadvantages =
1) uneven heating
2) Can have product mass loss
Describe the process of a hot water blancher
- Food is conveyed through a water tank/pipe
- Water may be agitated or sprayed
Hot water blancher
Descrive the advantaged and disadvantages
Advantages:
1 - energy efficient
2 - smaller floor space needed
Disadvantage:
1 - May get thermophilic bacteria contamination
Name 3 types of blanchers
1 - hot water blancher
2 - steam blancher
3 - drum blancher
What can be a disadvantage of blanching?
1 - Blanching losses: can result in a net gain or loss of weight in products
2 - Heat treatment reduces nutrients: this is a tradeoff with enzyme inactivation
How can you adapt blanching for different products?
1 - steam for leafy products
2 - hot water for products with harder texture
How can you optimize blanching for quality?
3 methods
1 - Measure enzyme activity -> adjust blanch time accordingly
2 - **Use small product geometry **-> minimize critical dimension
3 - Rapid heat exposure with rapid cooling afterwards
1 - makes sure to inactivate enzyme without over-blanching
